Instruments distributed control system

The third case study consists of a well-instrumented experimental distillation column that has been interfaced to an industrial distributed control system. In this... 

Finally, a well-instrumented experimental distillation column that has been interfaced to an industrial distributed control system was used to show the implementation of the techniques described in previous chapters in an actual on-line framework, using industrial hardware. In this case, the usefulness of data reconciliation, prior to process modeling and optimization, was clearly demonstrated. 

Most of the monitoring instruments specified in the GATS design package are simple and reliable, having been used extensively in the chemical industry. Control valves and monitors for temperature and pressure, as well as distributed control systems and PLCs, have also been widely used in industry. 

The distributed control system (DCS) hardware areas are often referred to as "process computer rooms." I/O Rooms contain the incoming and outgoing wiring, cables and data highway links, and often small transformers and other related electrical equipment. Often, additional space is needed for a master process engineering computer terminal/work station for process control system changes and for critical safety instrumented systems (SIS) for interlocks and emergency shutdowns. 

Volatile control instrumentation records (distributive control systems—DCS—data) perform complete system backup of data... 

The instrumentation of processing plants is fully computerized these days, and the use of distributed control systems (DCS) along with advanced network systems makes plant operations highly reliable. 

A central location where instrument leads are short is preferred. In modem facilities with distributed control systems, all units are controlled from a central control room with few operators. Only a few roving operators are available to spot trouble. It is desirable to deep process equipment a minimum of 8 m away from the control room. Any equipment and hydrocarbon-containing equipment should be separated by at least 15 m if possible. Most control rooms are designed with blastproof construction and have emeigency backup power and air conditioning. The room is pressurized to prevent infusion of outside air that may have hydrocarbon content in the explosive range. 

Before reaching the point of complete data integration as given above, there are intermediary levels of data integration that are beneficial to better analysis of data from process analyzers. The best case would be to have all the data in a human readable form that is independent of the application data format. Over the years several attempts have been made to have a universal format for spectroscopic data, including JCAMP-DX and extensible markup language (XML). Because many instrument vendors use proprietary databases, and there is not a universal standard, the problem of multiple data formats persists. This has led to an entire business of data integration by third parties who aid in the transfer of data from one source to another, such as between instruments and the plant s distributed control system (DCS). 

While this staged approach has long been recognized as deficient, it is defensible from a certain perspective. For example, it would be difficult for the control engineers to specify the instrumentation and the distributed control system (DCS) without knowing exactly what process it was intended for. Similarly, it would make no sense for the process engineers to request a control system design for all those flowsheets... 

Control And Data Acquisition (SCADA), Industrial PC systems, and Distributed Control Systems (DCS). Measurement and control systems and process management systems are often integrated together. Process Analytical Technology (PAT) is a special case implementing nonintrusive process instrumentation. 

A distributed control system is a system that is functionally integrated but consists of subsystems that may be physically separate and remotely located from one another. A shared display is an operator interface device such as a computer screen or video screen that is used to display process control information from a number of sources at the command of the operator. Most plants built since 1990 (and many older plants) use shared displays instead of instrument panels. 

Automated Computer controlled usually through a personal computer or programmable logic controller. Less frequently by a central control computer or as part of a distributed control system Better repeatability Better process control Lower operating labor costs Data gathering automatic although some analytical instrumentation may remain off line Some to all routine operations may be automated... 

Table 16.14, based on Navarrete (1995) and Page (1996), reports the number of different elements in the distributed control system (DCS) for the MPls in different types of plants. The average number of field instruments decreases as the scope of the project increases. 

Some familiarity with control hardware and software is required before we can discuss selection and tuning. We are not concerned with the details of how the various mechanical, pneumatic, hydraulic, electronic, and computing devices are constructed. These nitty-gritty details can be obtained Ifom the instrumentation and process control computer vendors. Nor are we concerned with specific details of programming a distributed control system (DCS). These details vary from vendor to vendor. We need to know only how they basically work and what they are supposed to do. Pictures of some typical hardware are given in Appendix B. 

Instruments vary widely in their design depending upon the purpose for which they are built. Common features include a source of radiation, a means of bringing the radiation and the sample of interest together in a ceU or probe, and a detector. In applications to process measurement perhaps the most distinctive feature is the sample interface. The source of radiation used and the detectors are similar and often identical to laboratory-based instmmentation. Almost all of today s instra-ments include data acquisition and control electronics together with a user interface in a computerized form. To obtain the optimum performance from analytical and control systems, links to distributed control systems for feed-back and feed-forward control are vital. 

Based on the tried and tested standard components of the SIMATIC range, the system offered is highly flexible and can be used in a distributed configuration in stable housings and can be moved from location to location. The integrated instrumentation and control system ensures safety by means of reliable monitoring and alarm functions. 

Instrumentation and control During 1994 and 95, tests will be carried out to demonstrate the reliability of the distributed control system. 

NOTE Instrumented systems in the process sector are typically composed of sensors (for example, pressure, flow, temperature transmitters), logic solvers or control systems (for example, programmable controllers, distributed control systems), and final elements (for example, control valves). In special cases, instrumented systems can be safety instrumented systems (see 3.2.72). 

Microcomputer-based subsystems are standard in most computer control systems available today. The digital subsystems are interconnected through a digital communications network. Such systems are referred to as distributed digital instrumentation and control systems because of the network approach used to monitor and control the progress. 

The basic characteristics of alarm systems have already been covered at length in Chapter IX. Since an alarm is one of the most fundamental issues in a control system, it will be discussed here again in this context. In this clause, focus will be on independent alarm systems that can be applied to critical applications independently of a programmable logic controller/distributed control system (PLC/DCS). In spite of so much technological developments and modem instrumentation and... 

Design steps for a safe system. ALARP, as low as reasonably practicable BPCS, basic plant control system DCS, distributed control system IPL, independent protection layer PLC, programmable logic controller SIS, safety instrumentation system. 

Centralized control approach. DCS, distributed control system ESD, emergency shutdown system HMJ, human—machine interface MIS, management information system PU, pro cessing unit SIL, safety integrity level SIS, safety instrumentation system. 

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